1. Field of the Invention
The present invention relates generally to a method and apparatus for detecting transducer head and disk contacts in a direct access storage device (DASD) and more particularly to a method and apparatus for maintaining file readback performance compensating for readback errors caused by head/disk interaction used with a data detection channel in a DASD having instabilities.
2. Description of the Prior Art
Computers often include auxiliary memory storage units having media on which data can be written and from which data can be read for later use. Disk drive units incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks.
Because the strength of the field arising from magnetic domains is exponentially dependent on the distance from the magnetic dipoles and their spatial frequency, magnetic recording systems have been moving toward ever smaller separations between the disks and the read/write transducer heads to achieve high linear densities.
Effective procedures for predictive failure analysis (PFA) are particularly needed for low-flying, small form-factor drives that see a range of operating conditions in the portable computing environment. In portable computing applications, the heads carried by low-flying sliders can come into contact with the disks in low-pressure situations, such as high altitudes or reduced cabin pressure in airliners. Reduced window margins and consequent bit shift errors indicate that the file will suffer, at best, a readback performance degradation and, at worst, a tribology problem at reduced pressures. In either case, the user should be warned of an impending problem.
As used in the following description and claims, the term gain of a phase lock loop (PLL) means gain or bandwidth of the PLL.